This invention relates generally to imaging systems and more particularly to systems and methods for reducing an artifact within an image.
In some computed tomography (CT) applications, an object can be scanned in a limited angular range. For example, the object may be long and rectangular such that there is too much attenuation for x-ray beams at large oblique incidence angles, or the object might be obstructed in some angular range. As another example, in electron microscopy, biological specimens in the form of thin slices can be scanned by electrons in a limited angular range because of strong attenuation of an electron beam at large oblique incidence angles.
There are many methods for reconstructing images from a plurality of projections. One of these methods is a Fourier method, which involves a transformation of projection data generated from the projections into a Fourier or frequency space. A plurality of points in the Fourier space for which there is no projection data are estimated by interpolation. The reconstruction is then obtained from the Fourier space by taking an inverse Fourier transform. From limited angle projection data generated by scanning the object in the limited angular range, one can calculate a plurality of frequency components in the limited angular range in the frequency space. A region in the frequency space where the frequency components of the object are known is an allowed sector and where a plurality of frequency components of the object are not known as a missing sector. However, an artifact or alternatively a plurality of artifacts are generated within an image that is reconstructed from the missing sector and the allowed sector.